1. Field of the Invention
The present invention relates to a VoIP (Voice on Internet Protocol) system, VoIP server and client, and a multicast packet communication method, and more particularly, to a VoIP system which transmits data such as paging data broadcasted concurrently and MOH (Music On Hold) data, in the form of multicast packets.
2. Description of the Related Art
There has been a known VoIP system which enables voice communications with use of an IP (Internet Protocol) network used for the Internet. For example, a VoIP system is constructed by connecting a VoIP server and plural clients to each other on an IP network. Under control from the VoIP server, voice communications are realized between the plural clients, using, as media, voice data decomposed into IP packets.
The prior art document relating to the VoIP system includes the following: JP-A-2001-230774 and JP-A-H04(1992)-192955.
In the conventional VoIP system described above, problems described below are expected in case of transmitting, as multicast packets, paging data broadcasted concurrently on the IP network and MOH data which notifies holding status upon a hold operation during voice communication.
For example, in case of paging, a client who executes paging transmits transmission data for the paging as multicast packets to all clients equally, regardless of whether the client who receives the paging can receive multicast packets or not. Alternatively, the client transmits paging data as unicast packets to every client that is a target receiver of the paging.
Also in case of MOH, a VoIP server transmits voice packets for the MOH, in the form of multicast packets, regardless of whether the receiver who receives MOH data is capable of receiving multicast packets or not. Alternatively, an internal sound source is provided in every client to let users hear MOH.
Therefore, there are clients in a network environment in which the clients cannot receive multicast packets due to any reason, such as clients connected to a router incapable of routing multicast packets. Those clients cannot receive transmission data of paging or MOH transmitted in the form of multicast packets from other clients or a VoIP server.
The foregoing problems in multicast packet communications in the VoIP system are not limited to the paging or MOH but are common to communications among three or more partners (e.g., telephone-communication conferences [conference call]), streaming, etc.